EXTENSION COUKSE IN SOILS. 81 



paratively level alluvial soils, which are not so fine in texture as to 

 make tillage for the development of good tilth and conservation of 

 moisture impossible. Sandy loams, loams, and silt loams are there- 

 fore better than heavy clay soils. The large amount of nourishment 

 required by this crop can bo supplied only by soils having high natural 

 fertility or by the use of fertilizers. The virgin fertility of the rich 

 black prairie soils has proved sufficient to meet the demands of this 

 crop for a number of years after being first broken, but in no case can 

 undiminished yields be expected to continue indefinitely without the 

 application of fertilizers. 



The study of the root system of corn is interesting. (Ref. No. 2, 

 pp. 215). As ordinarily planted in rows 3^ feet apart in a deep 

 permeable soil, the roots extend to a depth of 18 inches by the time 

 the crop is 1^ feet high and is about 6 weeks old. Even at this stage 

 the roots meet between the rows so that the entire subsoil is occupied. 

 When the corn has reached a height of 3 feet the roots often extend to 

 a depth of about 24 inches. 



Cotton (Ref. No. 7, pp. 695,696). — Ck)tton requires approximately 

 130 days to reach maturity and so is confined practically to the 

 region south of a line running from southegm Virginia to northern 

 Oklahoma. The lowland varieties of cotton require a longer season 

 than do the upland varieties. The requirements of cotton for water 

 and fertility are very similar to those of corn, and this crop gives 

 good yields on heavy soils well supplied with orgajnic matter in sections 

 where the rainfall is not too large. This is especially true in Texas. 

 In the Southeastern States, however, the most widely grown varieties 

 give best results on sandy loam soils. 



Tohacco (Ref. No. 7, pp. 699-701). — Tobacco is similar to corn and 

 cotton in its f ertihty requirements, except that it uses somewhat less 

 phosphorus than these crops. It requires large amounts of nitrogen 

 and potassium and must grow rapidly and thoroughly cover the 

 ground in order to develop the seK-shading which is necessary to the 

 fine texture o*f the leaf essential to the production of a good smoking 

 flavor. For this reason the soil must be kept in the highest state of 

 fertility, and there must always be an excess of the essential elements 

 in available form beyond that needed to supply the actual require- 

 ments of the growing crop. 



The texture of the soil also has an important influence on the quality 

 of the tobacco leaf. The finer textured wrappers are grown only on 

 loams and sandy loams, while the coarser textured fillers may be 

 grown on heavier soils, which produce larger yields, though of a lower 

 grade. Topography has an important bearing on the growth of 

 tobacco, since it influences humidity and danger of storms to which 

 this crop is especially subject. Shallow-dipping valleys in which the 



21862°— Bull. 355—16 6 



